Buffered formalin is the superior fixative for the detection of HPV DNA by in situ hybridization analysis

In situ hybridization is used commonly for detection of human papillomavirus (HPV) DNA. There is little information, however, on whether the detection of HPV DNA by in situ hybridization can be affected by the way in which the tissue is fixed. To address this question, the authors compared the hybridization signal using this technique under low stringency conditions for several genital condylomata containing HPV 6 or 11 that were randomly subdivided and fixed in various fixatives for 16 hours. In all cases, the largest proportion of cells with koilocytotic atypia that had detectable HPV DNA was in buffered formalin-fixed tissue (80%), followed by tissue fixed in unbuffered formalin (70%), Hartman's solution (40%), and Bouin's solution (10%). After a high stringency wash, the greatest decrease in the overall hybridization signal was with tissue fixed in Bouin's solution; a minimal decrease was noted with tissue fixed in buffered formalin. Fixation in Bouin's solution for 2 hours gave in situ hybridization results comparable with buffered formalin fixation but with poorer cytologic detail. It is concluded that, of the fixatives studied, buffered formalin is superior for the detection of HPV DNA by in situ hybridization analysis.